The present invention relates to a gate electrode structure which controls electron emission from a field emission type electron source, a method of manufacturing the same, and a flat panel display which has the gate electrode structure.
In recent years, as a flat panel display such as an FED (Field Emission Display) or a flat vacuum fluorescent display in which electrons emitted from an electron-emitting source serving as a cathode bombard a light-emitting portion formed of phosphors on a counterelectrode to emit light, various types that use nanotube fibers, e.g., carbon nanotubes or carbon nanofibers, as the electron-emitting source have been proposed (for example, see Japanese Patent Laid-Open Nos. 2002-343281 and 2004-193038). FIG. 15 shows an example of a conventional flat panel display which uses nanotube fibers as an electron-emitting source.
This flat panel display has a cathode substrate 120 having a substrate 121 made of glass or the like, an anode substrate 130 having a front glass 131, and a gate substrate 110 which is disposed substantially parallel to the substrate 121 and front glass 131. The substrate 121 of the cathode substrate 120 and the front glass 131 of the anode substrate 130 form an envelope. The interior of the envelope is held in a vacuum state.
The cathode substrate 120 further has a plurality of substrate ribs 122 which are formed parallel to each other on the substrate 121, and cathodes 123 which are formed in regions sandwiched by the substrate ribs 122 on the substrate 121 and substantially form matrices when seen from the top. As the cathodes 123, electron-emitting sources made of the nanotube fibers described above are used.
The anode substrate 130 further has a plurality of black matrices 132 which are formed on the front glass 131 to be parallel to the substrate ribs 122, phosphor films 133R, 133G, and 133B which are formed on regions sandwiched by the black matrices 132 on the front glass 131, metal-backed films 134 which are formed on the phosphor films 133R, 133G, and 133B to serve as anodes, and a plurality of front ribs 135 which are formed on the black matrices 132. The black matrices 132 serve to prevent leaking light emitted from adjacent phosphors so as to improve the contrast of the flat panel display. The black matrices 132 are desirably formed as thin as possible to prevent a decrease in luminance of the flat panel display. The front ribs 135 are also desirably formed thin.
The gate substrate 110 comprises a glass plate 111, a flat electrode 112 which is formed on the surface of the glass plate 111 on the anode substrate 130 side, band-like gate electrodes 113 formed on the surface of the glass plate 111 on the cathode substrate 120 side to correspond to the phosphor films 133R, 133G, and 133B, and an insulating layer 114 which is formed on the gate electrodes 113. The gate substrate 110 has electron-passing holes 115, substantially circular when seen from the top, which are formed at regions where the band-like gate electrodes 113 and matrix-like cathodes 123 overlap, and extend through the flat electrode 112, glass plate 111, gate electrodes 113, and insulating layer 114. The gate substrate 110 is sandwiched by the substrate ribs 122 of the cathode substrate 120 and the front ribs 135 of the anode substrate 130.
The flat electrode 112 in contact with the front ribs 135 protects the cathodes 123 and gate electrodes 113 from the influence of an electric field generated by the anodes. This can prevent an electric field from being generated by a potential difference between the gate electrodes 113 and the metal-backed films 134 which serve as the anodes, and prevent abnormal discharge between the cathodes 123 and metal-backed films 134, thus preventing leaking light.
In this flat panel display, when a predetermined potential difference is applied between the gate substrate 110 and cathodes 123 such that the gate substrate 110 side has a positive potential, electrons extracted from those regions of the cathodes 123 which intersect the gate electrodes 113 are emitted from the electron-passing holes 115.
More specifically, first, a voltage is applied to the flat electrode 112 to set it to have a higher potential than that of the cathodes 123, so as to form an electric field on the surfaces of the cathodes 123 in advance. When a voltage is further applied to the gate electrodes 113 to set it to have a higher potential than that of the cathodes 123, an electric field is formed on the cathodes 123 to extend from the outer surfaces of the gate electrodes 113 which form the electron-passing holes 115, to extract electrons from the electron-emitting sources on the surfaces of the cathodes 123. The electrons are accelerated by the flat electrode 112 to which the voltage has been applied to set it to have a positive potential with respect to the gate electrodes 113, and emitted from the electron-passing holes 115 toward the front glass 131.
If a positive potential (accelerating voltage) higher than that on the flat electrode 112 is applied to the metal-backed films 134, the electrons emitted from the electron-passing holes 115 are accelerated toward the metal-backed films 134, and penetrate through the metal-backed films 134 to bombard the phosphor films 133R, 133G, and 133B. Thus, the phosphor films 133G, 133B, and 133R emit light.
A method of forming the respective constituent elements of the flat panel display shown in FIG. 15 will be described.
The cathode substrate 120 is formed in the following manner. First, an insulating paste such as a vitreous paste is printed on the substrate 121 with a known printing method such as screen printing to form the substrate ribs 122 on one surface of the substrate 121. Subsequently, the cathodes 123 disposed with electron-emitting sources on their surfaces are disposed on those regions of the substrate 121 which are sandwiched by the substrate ribs 122. This forms the cathode substrate 120. The cathodes 123 described above can be formed by disposing the electron-emitting sources on their surfaces by CVD or the like.
The anode substrate 130 is formed in the following manner. First, the front glass 131 is prepared. An insulating paste such as a vitreous paste is printed on the front glass 131 with a known printing method such as screen printing to form the black matrices 132 on one surface of the front glass 131. Subsequently, a phosphor material is printed on those regions on the front glass 131 which are sandwiched by the black matrices 132 with a known printing method such as screen printing to form the phosphor films 133R, 133G, and 133B. The metal-backed films 134 are formed on the phosphor films 133R, 133G, and 133B with a known deposition method. Finally, a glass paste is repeatedly printed on the black matrices 132 with a known printing method such as screen printing to form the front ribs 135. Alternatively, the front ribs 135 may be formed by fixing members, e.g., strip-like glass plates, made of glass or a ceramic material into predetermined shapes, on the black matrices 132 by adhesion using a frit paste, or by contact bonding using a metal film.
The gate substrate 110 is formed in the following manner. First, the glass plate 111 is prepared, and the flat electrode 112 is formed on its one surface by printing or sputtering. Subsequently, the band-like gate electrodes 113 are formed on the other surface of the glass plate 111 by printing or sputtering. The insulating layer 114 is formed on the other surface of the glass plate 111 by printing or the like to cover the gate electrodes 113. Finally, the electron-passing holes 115 which extend through the flat electrode 112, glass plate 111, gate electrodes 113, and insulating layer 114 are formed by sandblasting.
In the flat panel display, a high luminance can be realized by increasing the amount of current (anode current) flowing through the anodes or the voltage (anode voltage) to be applied to the anodes. If the anode current is increased, the phosphors will decompose. Hence, to realize a high luminance, it is effective to increase the anode voltage. When the anode voltage is increased, the gate electrodes 113 and cathodes 123 cannot be electrically shielded completely due to the influence of the electric field generated in the anodes by the flat electrode 112, and abnormal discharge may occur between the anodes and the cathodes 123. To prevent this, the front ribs 135 must be formed such that the distance between the anodes and the flat electrode 112 is sufficiently large. For example, when the anode voltage is 10 kV, the distance between the anodes and the gate electrodes 113 is desirably about 3.0 mm.
As described above, the front ribs 135 form rods or plates which are very thin as compared to their lengths to prevent a decrease in luminance of the flat panel display. It is therefore difficult to form the front ribs 135 to predetermined heights with the conventional method of repeating printing. For example, when the front ribs 135 are to be formed with widths of about 200 μm, their heights are about 2.0 mm at most. When the front ribs 135 are to be formed with widths of about 50 μm, their heights are about 1.0 mm at most.
When the strip-like glass plates are to be fixed on the black matrices 132 by adhesion or contact bonding to form the front ribs 135, thin glass plates as thin as about 50 μm cannot be formed, and a high-resolution flat panel display cannot be obtained. Assume that comparatively thick glass plates are to be fixed by adhesion. Frit glass or a silver paste is used to fix the glass plates. Thus, even if the glass plates are arrayed on the black matrices 132 highly accurately, they are adversely affected by the thermal expansion of the front glass 131 or the like during annealing. Therefore, it is difficult to array the formed front ribs 135 highly accurately.